This is my current setup as of about yesterday (got the cables yesterday and the D12 last week). These cables are the Beat Audio - Supreme Elegance. For a more detailed review of the cable alone, try reading project86's review on it.
Previously I've been using the Quads with stock cables and the iBasso D10. It was a good match, but there was a lot of background noise, probably because the D10's were pouring too much into the sensitive Quads. There was always this bed of faint white noise in the background, which was constant and you eventually habituate to. However, there were those times between music (gaps) that were so quiet that you do hear and notice the noise again. I heard the D12's were much more silent and stable, thus went out and searched for one.
As a combo of the D12 and the cable, the Quads have gotten MUCH tighter IMO. the bass is clearly much tighter and hitting harder. I believe both the cable and the D12 are said to be "quite open and bright", therefore leading to my logic of pairing it with the smooth-treble Quads. Much better imaging and instrument, more crisp trebles. I might be getting more microdetails, but that may be a placebo, but the tightness and the more pronounced treble is clearly physical IMO. And as expected, the background is totally black and silent, no noise whatsoever until I turned the D12's volume knob up to 12 o'clock. For reference, I usually listen at around 8:45 o'clock volume, and 11 o'clock volume is ear-splitting and probably may bust the Quads drivers.
I tried comparing D12+stock cable with D12+Beat Cable, difference is pretty much close to described as above, but to a less magnitude. However, the bass tightness is clearly different here as well.
I do know there's a lot of controversy regarding cables and their improvements here, and I totally respect all opinions. For those who do believe in the cable influence, you may interpret this as a synergy/improvement due to the upgrade of both D10 to D12 and the stock cable to the Beat Audio. As for those who do not believe in such cable influence, you may take it as solely the improvement from upgrading the D10 to D12's.
Please do take this impression with a grain of salt, for these Quads are my first customs, and the beat cables are my first cables besides from the stocks that usually come with the phones. I haven't done much impressions before, but do hope what I'm saying here is getting the message through. The cables have not even reached 10 hours of use, and I doubt the D12's have reached 50 hours, much less 100 hours of use, so those who believe in burn-ins, please take this into consideration, YMMV.
Overall, am very pleased with my choice so far, starting with the Quads, then the D10 --> D12 upgrade, then the Beat Audio cable upgrade. Next goal is to get a better USB cable than the current stocks to pair with this awesome combo. Will update you guys if any progress comes up.